The present invention relates to a system for transmitting digital data over a variety of communications media.
Ethernet protocol has seen tremendous growth in the past few years. Video compression techniques such as MPEG, JPEG, H264 are also in larger and larger demand. A wide variety of applications are expected to be based on video compression techniques including: surveillance cameras in grocery stores and parking lots, Internet imaging, IP video, and cameras for underground or underwater exploration. Due to technology limits, Ethernet protocol and compressed digital video communications are currently supported on only a limited number of physical media. New technology advancements proposed herein make possible the use of Ethernet protocol and compressed and uncompressed digital video with a variety of communication media.
One digital signal processing technique suitable for transmitting video over a variety of communications media is called orthogonal frequency division multiplexing (OFDM). OFDM is used in the telecommunications industry with multi-modulated carrier frequency transmission and reception. OFDM can be combined with adaptive coding and modulation techniques, such as 64QAM, 32QAM, 16QAM, QPSK and BPSK modulation. In order to approach channel capacity, a certain signal-to-noise ratio (SNR) is required for each coding and modulation combination to achieve a desired bit error rate (BER) performance. Even higher SNRs are needed if the system uses a larger alphabet size for achieving a higher data rate. Adaptive coding can also be used with OFDM to combat SNR variations. For example, when the signal is heavily attenuated through the channel, the same data can be repeated several times to boost the SNR at the receiver end for a reliable data recovery. However, repeating the data reduces the throughput of the communication system.
Other digital signal processing techniques include spread spectrum, quadrature phase shift keying (QPSK); phase shift keying (PSK); 16, 32 and 64 quadrature amplitude modulation (xxQAM); frequency shift keying (FSK), and frequency offset keying modulation.
In order to achieve desired SNRs for reliable communication and to keep the throughput high, the digital data stream may be frequency modulated before transmission and frequency demodulated before being decoded. Frequency modulating the digital data stream gains 10-20 dB in SNR. resulting in: (1) significantly longer distance communication without increasing the transmit power level and (2) significantly higher throughput to maintain high speed through the communication media. Suitable communication media includes but is not limited to AC and DC power lines, wireless media, cable, telephone lines, twisted pairs, and coaxial cable. DC power line communications includes the communication over the DC wiring harness of moving vehicles like trucks, buses, SUV's and etc. With the advantage of using frequency modulated digital signal processing, Ethernet protocol and compressed or uncompressed digital video with or without audio from a digital camera, digital camcorder, monitor or TV input can be supported over all the above mentioned media.
Frequency offset (ON/OFF) keying is another digital modulation technique that is being used in the communication industry. Differential frequency offset keying (FOK) can improve the SNR through the communication media. Furthermore multiple FOK modulated carrier frequencies can be used to create frequency division multiplexing (FDM) or OFDM where, instead of using QPSK, BPSK, or 16QAM modulation, FOK modulation can be used for multi modulated carrier frequencies. This can further improve SNR by using the frequency modulated DSP technique, where FOK modulation is used for the carrier frequencies.